Air Pressure & Wind Chapter 19 “The Atmosphere in Motion”

Air Pressure the weight of the atmosphere pushing down on the Earth exerting a force per unit area exerted in all directions decreases with elevation

Measuring Air Pressure Barometers measure air pressure Two Types: ◦ Mercury ◦ Aneroid Units: ◦ inches & millimeters used in mercury ◦ millibars

Talk with a partner: When have you experienced a change in air pressure?

Factors Affecting Air Pressure 1. Temperature ◦ as temperature increases, air pressure decreases ◦ Molecules move farther apart 2. Humidity ◦ as humidity increases, air pressure decreases ◦ water vapor has less mass than air

Air Pressure on Weather Maps Isobars are lines that connect areas of equal air pressure connected areas form patterns and allow us to view weather patterns closely spaced isobars indicate rapid pressure change

Highs & Lows when air pressure is greater at the center than the outside we have a high when it is lower, we have a low

The Air in Highs & Lows High Pressure Low Pressure sinking air usually colder, dry air brings fair weather clockwise away from center rising air warmer, humid air usually brings storms c. clockwise towards center

Talk with a partner: What are the differences in H and L pressure?

Wind moderates temperature, distributes moisture, cleanses atmosphere named for the direction in which they came created by differences in air pressure blow from H  L pressure atmosphere

Measuring Wind Anemometer measures wind speed in mph or kph Wind Vane measures wind direction

Air Pressure & Wind A pressure gradient is change in air pressure divided by the distance over which the air pressure changes The greater the pressure gradient, the stronger the wind blows between two points

Sea Breeze land heats up faster than ocean air over land rises cooler, denser air from over ocean blows in to replace rising air

Land Breeze reverses at night ocean holds heat from day, land loses it quickly breeze switches

Sea and Land Breezes SEA BREEZE day time LAND BREEZE night time

FACTORS AFFECTING WINDS

1. The Coriolis Effect the tendency of an object moving over the Earth’s surface to curve away from its path of travel caused by Earth’s rotation greater near poles increases as speed of object increases Noticeable for objects traveling over great distances (i.e. planes, winds, ocean currents)

The Coriolis Effect N. hemi  deflected to right S. hemi  deflected to left

The Coriolis Effect & Winds Winds blow clockwise OUT of a high pressure center Winds blow counterclockwise INTO a low pressure center This is the reverse of the Southern hemisphere

High 5 & Share: Do you think the Coriolis Effect would have any affect on Land and Sea Breezes? Why or why not?

2. Friction smoother the surface, faster the winds faster the winds, the stronger the Coriolis Effect This means the Coriolis Effect has a lesser effect on surface winds than upper atmosphere winds (there’s less friction in the upper atmosphere)

3. Time of Year [air flows from high to low pressure] H and L pressure have temp differences temp. varies throughout year, based on amt. of insolation so winds change seasonally

The Jet Stream bands of very strong winds in the upper troposphere thousands of kilometers long, hundreds wide, and one kilometer tall polar-front jet stream controls our weather and brings cold air from the poles fastest in the winter

Convection Cells continuously heat atmosphere create global winds as air moves away from highs and towards lows

Global Wind Patterns if the Earth did not rotate, we’d have one large convection cell Hot air rises at the equator, cools, then sinks at the poles and flows back down to the equator

Global Wind Patterns Because the Earth does rotate the Coriolis Effect changes this convection cell Air cools long before it reaches the poles 3-celled circulation model is used

3-Celled Circulation Model circulation cells are caused by alternating high and low pressure bands at the surface also called Hadley cells Winds deflect to the right in the Northern hemisphere

Intertropical Convergent Zone (ITCZ) Area where the surface winds of the two hemispheres converge hot, humid, little to no wind present also called doldrums

Trade Winds area between 30º and 0º in each hemisphere steady winds location where merchants wanted to sail their ships

Effect of Global Wind Patterns Precipitation patterns are effected. deserts at mid-latitudes & on leeward side of mountains